全文获取类型
收费全文 | 4814篇 |
免费 | 462篇 |
国内免费 | 2篇 |
专业分类
5278篇 |
出版年
2023年 | 18篇 |
2022年 | 54篇 |
2021年 | 119篇 |
2020年 | 73篇 |
2019年 | 86篇 |
2018年 | 81篇 |
2017年 | 77篇 |
2016年 | 154篇 |
2015年 | 240篇 |
2014年 | 253篇 |
2013年 | 291篇 |
2012年 | 423篇 |
2011年 | 423篇 |
2010年 | 259篇 |
2009年 | 194篇 |
2008年 | 329篇 |
2007年 | 348篇 |
2006年 | 266篇 |
2005年 | 299篇 |
2004年 | 269篇 |
2003年 | 228篇 |
2002年 | 236篇 |
2001年 | 33篇 |
2000年 | 45篇 |
1999年 | 54篇 |
1998年 | 60篇 |
1997年 | 35篇 |
1996年 | 30篇 |
1995年 | 28篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1987年 | 7篇 |
1986年 | 14篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 14篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1974年 | 9篇 |
1972年 | 6篇 |
1967年 | 6篇 |
1966年 | 6篇 |
1965年 | 6篇 |
排序方式: 共有5278条查询结果,搜索用时 15 毫秒
11.
Thermoregulatory control during pregnancy and lactation in rats 总被引:1,自引:0,他引:1
Eliason, Heather L., and James E. Fewell.Thermoregulatory control during pregnancy and lactation in rats.J. Appl. Physiol. 83(3): 837-844, 1997.Although the mechanisms remain unknown, maternal coretemperature (Tc) decreases nearterm of pregnancy and is increased throughout lactation in rats. Thepurpose of our present experiments was to determine whether pregnancy and lactation shift the thermoneutral zone of rats and to investigate whether the changes in maternal Tcduring pregnancy and lactation result from "forced" or"regulated" thermoregulatory responses. Conscious, chronicallyinstrumented nonpregnant and pregnant and lactating rats were studiedboth in a thermocline (a chamber with a linear temperature gradientfrom 12 to 36°C) and in a metabolic chamber to determine theinfluence of pregnancy and lactation on selected ambient temperature aswell as the thermoregulatory response to changes in ambienttemperature. We found that selected ambient temperature, oxygenconsumption, and thermal conductance did not change in rats studied ina thermocline as Tc decreased nearterm of pregnancy. There was, however, a downward shift in thethermoneutral zone of rats studied in a metabolic chamber near term ofpregnancy. During lactation, selected ambient temperature decreased inrats studied in a thermocline as oxygen consumption andTc increased. The thermoneutralzone of lactating rats was not different from that of nonpregnantanimals. Thus our data provide evidence that the decrease inTc near term of pregnancy in ratsresults from a regulated thermoregulatory response,whereas the increase in Tc duringlactation results from a forced thermoregulatory response. 相似文献
12.
13.
James R. White Heather N. Yeowell 《Biochemical and biophysical research communications》1982,106(2):407-411
The lethal action of streptonigrin on strains of is greatly enhanced by citrate (10?2 M). Desferrioxamine (2×10?4 M), when added with streptonigrin and citrate, eliminates the citrate enhancement. These observations point to a role for iron in the bactericidal mechanism of streptonigrin. Extracellular citrate is known to promote the acquisition of iron by by delivering it as a ferric citrate complex to a specific transport apparatus on the cell envelope. Therefore, it may promote action of streptonigrin by increasing the intracellular concentration of available iron. Desferrioxamine, which forms a much stronger complex with ferric ion than does citrate, would be expected to suppress the ferric citrate effect, and this was observed. 相似文献
14.
Enterobacteriaceae and Aeromonas hydrophila in Minnesota frogs and tadpoles (Rana pipiens) 总被引:1,自引:0,他引:1
D W Hird S L Diesch R G McKinnell E Gorham F B Martin C A Meadows M Gasiorowski 《Applied and environmental microbiology》1983,46(6):1423-1425
In 222 Rana pipiens frogs and 34 tadpoles captured in and near Minnesota, Aeromonas hydrophila and 29 species of Enterobacteriaceae, including yersinia enterocolitica and Salmonella arizonae, were isolated from intestines. The prevalence of members of the family Enterobacteriaceae was lowest in frogs captured in early spring and highest in frogs captured in late summer. 相似文献
15.
16.
Heather Windle 《BMJ (Clinical research ed.)》1980,280(6229):1425-1426
17.
18.
19.
Anna Reuleaux Heather Richards Terence Payet Pascal Villard Matthias Waltert Nancy Bunbury 《Ostrich》2014,85(3):245-253
Feeding ecology is an important factor for the survival of a species and knowledge of its parameters is a prerequisite for successful conservation work. In this study we describe the feeding ecology of the endemic Seychelles Black Parrot Coracopsis barklyi on Praslin, Seychelles, the only island on which this parrot is resident. We compared two methods to evaluate feeding choices: incidental observations and feeding walks on 25 transects in all habitat types. Black parrots fed on 46 different species, bringing the total number of known food plants to 53 species. They predominantly consumed endemic and native species (58% of observed feeding bouts), mainly their fruit pulp (in 68% of feeding bouts), followed by buds (15%) and seeds (37%) with occasional observations of leaves, bark and scale insects. The incidental method rendered many more observed bouts than the transect approach and the ratios of consumed species differed between methods but the transect results are regarded as more representative. The incidental method is not suitable for quantitative conclusions but complements the transect method, providing information about rarely occurring feeding events. 相似文献
20.